Aerodynamic airflow is a significant consideration during vehicle body design. Effective airflow management over a vehicle body can assist in meeting functional demands for passenger compartment acoustics, fuel efficiency, and safety of passenger type vehicles. Aerodynamic designs can also enhance vehicles control and improve speed of passenger vehicles. To reduce aerodynamic drag experienced at a vehicle at mid-high vehicle speeds, and to reduce the associated drop in fuel economy, vehicles may be configured with air deflectors or “active air dams”. These aerodynamic features are actuated between deployed and retracted (or stowed) positions and are used to deflect airflow around a vehicle frame, thereby limiting front end lift, and creating down-force. For example, when deployed, active (front) air dams (AAD) limit motor vehicle front end lift by creating a down-force, forcing the vehicle nose down, and thereby improving vehicle handling and stability. Front air dams may also assist in engine cooling. Other air deflectors, such as spoilers, can provide a similar effect, for example by creating a down force near a vehicle rear end to improve rear wheel contact with a road surface.
Over time and varying vehicle operating conditions, the mechanisms that deploy and stow the active air dams (e.g., linkages) may degrade. This can leave the air dam stuck in a deployed position when commanded to retract, or leave the air dam stowed when commanded to deploy. In this situation, aerodynamic drag may be increased, and fuel economy may be adversely impacted. Therefore, it may be desirable to determine whether or not the hardware associated with active air dams are operating as desired.
Various approaches have been identified for diagnosing degradation in AAD systems. One example approach is shown by Shami in U.S. Pat. No. 9,849,924. Therein, the engine control system relies on feedback from a plurality of speed and position sensors to infer AAD functionality. Still other approaches may rely on position feedback sensors coupled to the active air dams. Feedback from position sensors may be used to confirm if the air dam has deployed when actuated to deploy, and retracted when actuated to retract. For example, in U.S. Pat. No. 10,081,400, Azizou et al. rely on one or more of a position, a drawn current draw, and a back-electromotive force (back-EMF) of an AAD actuator to perform on-board diagnostics. In still further examples, Hall effect sensors may be used.
However, the inventors herein have recognized potential issues with such systems. As one example, there may be multiple modes associated with degraded AAD functionality that are not detectable via the above-mentioned sensors. For example, if Hall effect sensors are damaged or become contaminated from the environment, a AAD position may be unavailable, and the diagnostic may not be reliable. As yet another example, the AAD (e.g., the shutter, the linkage, or the sensor) may freeze due to ice accumulation. In such a situation, it may be difficult to distinguish between a degraded sensor and a degraded AAD shutter. As still another example, the AAD shutter may be stuck (in a retracted or deployed position) while the sensors are still functional. Alternatively, the AAD shutter may be functional while the sensors are degraded. In either case, the sensor signal may be unreliable for diagnostics. Consequently, an alternate method that supplements the sensor-based approach may be required to confirm AAD functionality reliably.
In one example, the issues described above may be at least partly addressed by a method including, during steady-state vehicle cruising, commanding a transition of an aerodynamic mechanism, coupled to a body of the vehicle, between a more deployed and a more retracted position; and indicating degradation of the mechanism responsive to fuel usage change of an engine of the vehicle following the commanding. The fuel usage change may be assessed in relation to a baseline established while operating the engine with an active air dam system of the vehicle in the deployed position. In one example, the more deployed position is a fully deployed position and the more retracted position is a fully retracted position of the air dam. In this way, a reliable diagnosis of AAD functioning may be made and degradation of the AAD hardware may be identified.
As an example, a vehicle may be propelled at a steady mid-to-high speed level with the engine in steady-state operation (e.g., during highway cruising). In particular, the vehicle may be at a speed level where the AAD system is fully deployed. A controller of the vehicle may calculate a resulting first fuel economy during the AAD-deployed mode. If the AAD mechanisms are not degraded, the first fuel economy calculated during the AAD deployed mode may be similar to or equal to a baseline fuel economy. The baseline fuel economy may be determined when the AAD mechanism is intact and functional, such as following manufacture of the vehicle. Then, while still in the steady-state operation, the AAD system may be transitioned to a fully retracted position. A second fuel economy may be calculated while operating in the AAD-retracted mode. The switch in AAD operation may result in an expected change (e.g., a decrease) in the second fuel economy of the vehicle from both the baseline fuel economy and the first fuel economy calculated, if the AAD mechanism is not degraded. However, if the calculated second fuel economy remains unchanged (e.g., does not decrease), despite the commanded change, the AAD mechanism may be determined as degraded. Further, if the determined second fuel economy is found to be within a threshold of the baseline fuel economy, the VDE may be confirmed as stuck in the AAD-deployed mode. Likewise, if the determined first fuel economy is found to be outside a threshold of the baseline fuel economy, the VDE may be confirmed as stuck in the AAD-retracted mode
In this way, an AAD system can be independently diagnosed without the need for additional sensors. By comparing the fuel economy of an engine with the AAD hardware deployed or retracted with a baseline fuel economy established while the AAD system is confirmed to be functional, the impact of AAD adjustments on fuel economy can be leveraged for diagnosing the AAD system. By correlating the results of a fuel economy based diagnostic test with sensor data, lack of AAD functionality due to AAD hardware degradation can be better distinguished from sensor degradation. By allowing an AAD system to be timely and reliably diagnosed, the fuel economy benefits of the system can be extended over a longer duration of vehicle operation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.